Office 365 is planning to discontinue support for basic auth on services like POP and IMAP on October 13, 2020. As of today, basic auth (username and password) via IMAP/POP is the only way to make Jira able to use an Office 365 mailbox for receiving email. More details about the upcoming changes to Microsoft's products can be found in https://developer.microsoft.com/en-us/office/blogs/end-of-support-for-basic-authentication-access-to-exchange-online-apis-for-office-365-customers/
Implement some other method of allowing Jira to authenticate to an office 365 mailbox, such as OAuth2.
Without this feature, regular office 365 accounts won't permit applications like Jira to connect to them. It seems that the ProPlus accounts might still permit this after the set date, however it seems clear that improving security is the goal of this forced change, and perhaps it would benefit Jira to follow suit.
None currently, if one should become available this will be updated to reflect that state.